Implantable medical devices are available for treating cardiac arrhythmias by delivering anti-tachycardia pacing therapies and electrical shock therapies for cardioverting or defibrillating the heart. Such a device, commonly known as an implantable cardioverter defibrillator or “ICD”, conventionally senses a cardiac signal to determine a patient's heart rate and classifies the rate according to a number of heart rate zones in order to detect episodes of ventricular tachycardia (VT) or ventricular fibrillation (VF). A number of rate zones may be defined according to programmable detection interval ranges for detecting slow ventricular tachycardia, fast ventricular tachycardia and ventricular fibrillation. Intervals between sensed R-waves, corresponding to the depolarization of the ventricles, are measured. Sensed R-R intervals falling into programmable detection interval ranges are counted to provide a count of VT or VF intervals. A programmable number of intervals to detect (NID) define the number of tachycardia intervals occurring consecutively or out of a given number of preceding event intervals that are required to detect VT or VF.
In some ICDs, tachyarrhythmia detection may begin with detecting a fast ventricular rate, referred to as a rate- or interval-based detection. Once VT or VF is detected based on rate, the morphology of the sensed depolarization signals may be analyzed to discriminate between heart rhythms to improve the sensitivity and specificity of tachyarrhythmia detection methods and therapy decision-making. For example, before a therapy decision is made, tachyarrhythmia detection may require discrimination between supraventricular tachycardia (SVT) and VT using cardiac signal waveform morphology analysis or other higher level cardiac signal analysis, particularly when a fast 1:1 atrial to ventricular rate is being sensed.
Programmable parameters for controlling the detection process may set various thresholds, boundaries, or other detection criteria to be applied to RR intervals and cardiac signal morphology for detecting and discriminating SVT, VT and VF. With the advancement of tachyarrhythmia detection methods, numerous features of an intracardiac electrogram (EGM) or ECG signal may be analyzed to enhance the sensitivity and specificity of tachyarrhythmia detection. The burden on the clinician in programming an ICD is increased with an increasing number of features to be analyzed and corresponding detection thresholds to be programmed. In some ICDs, upwards of hundreds of parameters controlling ICD function may be programmable. The complexity and sheer number of programmable parameters may lead to programming error, potentially resulting in unneeded therapies being delivered or a lack of therapy when it is needed. The programming burden placed on a clinician or technical support staff is considerable. The availability of ICDs to patients in some geographical regions may be limited due to a lack of local technical expertise required in programming the device. A need remains, therefore, for ICD systems that address and alleviate the burden and complexity of programming ICD control parameters.